This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application No. 11(1999)-265702 filed on Sep. 20, 1999, the entire content of which is incorporated herein by reference.
The present invention generally relates to a refrigerator. More particularly, the present invention pertains to a pulse tube refrigerator having improved cooling efficiency or cooling power.
Recent research and development of a pulse tube refrigerator has led to the development of a supercooling refrigerator. The pulse tube refrigerator provides cooling by using adiabatic expansion of an operating gas in a pulse tube refrigerator.
Various types of pulse tube refrigerators are disclosed in publications concerning cooling technology (e.g., ISTEC Journal, Vol.9, No.3 xe2x80x9cPulse Tube Cryocoolerxe2x80x9d).
One traditional type of pulse tube refrigerator is shown in FIG. 7. As shown in FIG. 7, this pulse tube refrigerator 81 includes a compressor 82, a cooling device 83, a regenerator 84, a cold head 85, a pulse tube 86, a radiator 87, an orifice 88, and a buffer tank 89, which are connected in series. A cooling part 90 is accommodated in a vacuum vessel 81a and consists of the cooling device 83, the regenerator 84, the cold head 85, the pulse tube 86 and the radiator 87.
The compressor 82 includes a compression cylinder 91 and a compression piston 92 that is positioned in the compression cylinder 91 for reciprocating movement. A compression chamber 93 is defined between a front surface of the compression piston 92 and the cooling device 83. The compressor 82 moves by applying a driving force generated by a driving unit such as a motor (not shown in FIG. 7) so that the compression piston 92 reciprocates in the compression cylinder 91. An operating gas in the pulse tube refrigerator 81 is thus compressed and expanded alternately.
Heat generated in the pulse tube refrigerator 81 is conducted to the cooling device 83 and the radiator 87, and is heat exchanged therein. The heat exchanged by the cooling device 83 is discharged to a coolant flowing in a first cooling path 94. The heat exchanged by the radiator 87 is discharged to a coolant flowing in a second cooling path 95.
Regenerative material 96 is located in the regenerator 84 for effecting heat exchange of the operating gas. A plurality of layered mesh screens made of stainless steel or phosphor bronze may be used as the regenerative material 96. When the operating gas flows from the hot end of the regenerator 84 which is connected with the cooling device 83 to the cold end of the regenerator 84 which is connected to the cold head 85, the operating gas is cooled by discharging heat to the regenerative material 95. When the operating gas flows from the cold end of the regenerator 84 to the hot end of the regenerator 84, the operating gas is heated by absorbing heat from the regenerative material 96.
The cold head 85 is connected to the cold end of the regenerator 84. A cooling object attaches with the cold head 85 and the object is cooled.
The pulse tube 86 is connected to the cold head 85. The pulse tube 85 is a hollow cylindrical tube and is generally made of stainless steel.
The radiator 87 is connected to the buffer tank 89 via the orifice 88. The buffer tank 89 and the orifice 88 are used as a phase shifter, which adjusts the amount of phase difference between a pressure oscillation and a displacement of the operating gas.
The operation of the pulse tube refrigerator is described below. As the compressor 82 is driven, the compression piston 92 reciprocates in the compression cylinder 93. When the compression piston 92 moves forward, the operating gas in the compression chamber 93 and the cooling part 90 connected to the compression chamber 93 is compressed and moves from the compression chamber 93 to the cooling part 90. When the compression piston 92 moves rearward, the operating gas in the compression chamber 93 and the cooling part 90 expands and the operating gas in the cooling part 90 moves from the cooling part 90 to the compression chamber 93.
By repeating the reciprocating movement of the compression piston 92 in the compression cylinder 91, the pressure in the pulse tube 86 alternately oscillates from high pressure to low pressure and the operation gas moves reciprocally in the pulse tube 86. Then, an amount of the phase difference between the pressure oscillation and displacement of the operating gas in the pulse tube 86 is adjusted by the buffer tank 89 and the orifice 88. Therefore, the operating gas in the pulse tube 83 moves to the hot end side of the pulse tube 86 and is adiabatically compressed at the hot end. After that, it moves to the cold end side of the pulse tube 86 and is adiabatically expanded at the cold end. The heat generated by the substantially adiabatic compression at the hot end of the pulse tube 86 is conducted to the radiator 87 and is heat exchanged. The cold generated by the substantially adiabatic expansion at the cold end of the pulse tube 86 is conducted to the cold head 85. By repeating the operation described above, cold is generated at the cold head 85.
The traditional type of pulse tube refrigerator described above is inferior to a Stirling type refrigerator with respect to its cooling power. The Stirling type refrigerator has an expansion piston and the expansion work of the operation gas in the Stirling type refrigerator can be used to move the expansion piston. On the contrary, the traditional pulse tube refrigerator does not utilize the expansion piston. Therefore, the expansion work of the operating gas in the pulse tube refrigerator is changed to heat and the heat is discharged to the atmosphere by the radiator. Because the expansion work of the operating gas in the pulse tube refrigerator cannot be used as the work that contributes to generating the cold, the cooling power of the pulse tube refrigerator is inferior to the cooling power of the Stirling type refrigerator.
A need thus exists for a pulse tube refrigerator having improved cooling power.
One aspect of the present invention involves a pulse tube refrigerator that includes a series of cooling parts having one end side and an opposite end side, and a pressure oscillation source. Each cooling part is comprised of at least a regenerator, a cold head, and a pulse tube which are connected in series. The pressure oscillation source is connected to one of the cooling parts disposed at one end side of the series.
The expansion work generated in one cooling part can be used as compression work of the other cooling part that is connected to the one cooling part. The compression work of the other cooling part contributes to generate cold. Therefore, the expansion work of the operating gas in one cooling part can be used efficiently for cold generation in the other cooling part, and an improvement of the cooling power can be achieved.
The cooling parts include a first cooling part and a second cooling part. The first cooling part is defined by at least a first regenerator, a first cold head, and a first pulse tube. The first regenerator possesses a hot end and a cold end, and the hot end of the first regenerator is connected to the pressure oscillation source. The first cold head is connected to the cold end of the first regenerator. The first pulse tube has a hot end and a cold end, and the cold end of the first pulse tube is connected to the first cold head. The second cooling part includes at least a second regenerator, a second cold head, and a second pulse tube. The second regenerator has a hot end and a cold end, and the hot end of the second regenerator is connected to the first pulse tube. The second cold head is connected with the cold end of the second regenerator. The second pulse tube has a hot end and a cold end, and the cold end of the second pulse tube is connected to the second cold head.
Because the first pulse tube (i.e., the hot end of the first pulse tube) of the first cooling part is connected with the hot end of the second regenerator of the second cooling part, the expansion work generated in the first cooling part (i.e, the hot end of the first pulse tube) can be used as the compression work for the second cooling part. Also, the compression work of the second cooling part contributes to generate cold in the second cooling part. Therefore, the expansion work of the operating gas in the first cooling part can be used efficiently for cold generation in the second cooling part, and an improvement of the cooling power can be achieved.
A first cooling device and a first radiator may be attached in order to discharge heat generated in the first cooling part. The first cooling device can be disposed at the portion which contacts the hot end of the first regenerator. The first radiator is preferably disposed at a portion contacting the hot end of the first pulse tube.
A second cooling device and a second radiator may be attached in order to discharge heat generated in the second cooling part. The second cooling device can be disposed at the portion which contacts the hot end of the second regenerator, and the first radiator can be used for the second cooling device. The second radiator is preferably disposed at a portion contacting the hot end of the second pulse tube.
According to another aspect of the invention, a pulse tube refrigerator having a pressure oscillation source includes a first regenerator possessing a hot end connected to the pressure oscillation source and a cold end, a first cold head connected with the cold end of the first regenerator, and a first pulse tube having a hot end and a cold end, with the cold end of the first pulse tube being connected to the first cold head. The first regenerator, the first cold head and the first pulse tube form a first cooling part. A second regenerator possesses a hot end and a cold end, with the hot end of the second regenerator being connected to the hot end of the first pulse tube. A second cold head is connected to the cold end of the second regenerator, and a second pulse tube having a hot end and a cold end is connected to the cold end of the second cold head. The second regenerator, the second cold head and the second pulse tube form a second cooling part.
Another aspect of the invention involves a pulse tube refrigerator that includes a first cooling part having a regenerator, a cold head and a pulse tube arranged in series, with the pulse tube being adapted to generate expansion work of operating gas in the first cooling part, and a second cooling part connected to the first cooling part, with the expansion work of the operating gas generated by the first cooling part being used as the compressor for operating gas in the second cooling part.